Traditional spinal fixation, which is often referred to as rigid fixation, involves immobilizing spine segments (e.g., vertebrae) using a rigid spine stabilization rod that is connected between. Generally speaking, such a rigid spine stabilization rod is solid and has a uniform cross-section shape. One known drawback of such rigid fixation is an increase in motion of adjacent spine segments. Undesirably, this increased motion can impart significant unintended strain on to these adjacent spine segments and lead to further injury and pain. Therefore, spine stabilization rods and rod assemblies that offer a controlled amount of flexibility are beneficial, desirable and useful in spine fixation applications.